1. Field of the Invention
The present invention relates to a microfiche positioning mechanism for moving a microfiche along two perpendicular directions so that selected portions of the microfiche can be positioned in the optical path of a microfiche projection apparatus.
2. Discussion Related to the Problem
Microfiche is a cut-sheet form of microfilm, usually in a 4".times.6" rectangular format. Rows and columns of microimages are formed on the sheet, normally at reduction ratios of approximately 20.times. or 24.times.. There are normally sixty such microimages on a microfiche at 20.times. and ninety-six at 24.times. reduction. The microimages are enlarged in a projection apparatus for viewing and/or printing. Usually, the microfiche is placed in a holding frame or carrier in such apparatus and the carrier is positioned by hand to select the desired microimage for projection.
One problem with most prior art X-Y positioning mechanisms for microfiche is that they exhibit a characteristic "stick-slip" feel caused by friction. When a force is applied to such prior art positioning mechanism, they initially resist movement (i.e. stick) then suddenly lurch (i.e. slip) to a new position. This "stick-slip" behavior makes it difficult to smoothly achieve accurate positions--causing the operator to overshoot a desired position, and resulting in "hunting" for the final position. Another problem associated with prior art X-Y positioning mechanisms is their size. In order to place all the microimages carried by the microfiche into the optical path of the projection mechanism, it is necessary to displace the microfiche over an area approximately four times the area of the fiche itself. Even in some prior art "compact" microfiche readers, the positioning mechanism covers approximately four times the area of one fiche. See for example U.S. Pat. No. 3,563,645 issued Feb. 16, 1971 to F. A. Burke et al. Thus the problem faced by the inventor is to provide a smoothly operating, compact X-Y positioning mechanism for a microfiche projection apparatus.